Host Plant Resistance to Pests

11 Insect Antifeedants and Repellents from African Plants I. KUBO and K. NAKANISHI

Downloaded by MICHIGAN STATE UNIV on March 1, 2013 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0062.ch011

Department of Chemistry, Columbia University, New York, NY 10027

There is little doubt t h a t the tropical flora which a r e c o n s t a n t l y exposed t o a t t a c k by v a r i o u s p a r a sites such as v i r u s e s , b a c t e r i a , p r o t o z o a n s , f u n g i , and i n s e c t s a r e c o n f r o n t e d w i t h much h a r s h e r c o n d i t i o n s f o r survival than their temperate c o u n t e r p a r t s . T h i s necessarily leads to efficient built-in defense mechanisms and it is presumably f o r this r e a s o n t h a t tropical flora o f f e r a rich and intriguing source f o r isolating natural products possessing attractive pesticidal or medicinal properties. The results o u t l i n e d in the f o l l o w i n g stem from the s t u d i e s initiated in 1974 and more s y s t e m a t i c a l l y i n mid-1975 a t the I n t e r n a t i o n a l C e n t r e o f I n s e c t P h y s i o l o g y and E c o l o g y (ICIPE), N a i r o b i , Kenya. The g e n e s i s o f this unique c e n t e r goes back t o 1968 when C a r l D j e r a s s i (1) proposed a p l a n f o r establishing an international institute i n a d e v e l o p i n g country and Thomas R. Odhiambo, P r o f e s s o r o f Entomology a t the U n i v e r s i t y o f N a i r o b i , responded enthusiastically to initiate an i n s e c t o r i e n t e d institute in Nairobi. ICIPE was i n a u g u r a t e d in e a r l y 1970 w i t h generous s u p p o r t from the U n i t e d N a t i o n s Development Program, various o t h e r f o u n d a t i o n s , and f e d e r a l governments. Of a total of about 130 p e r s o n n e l c u r r e n t l y a t the C e n t r e , 25 are R e s e a r c h S c i e n t i s t s (post P h . D . ' s ) , m o s t l y b i o l o g i s t s , from a l l over the w o r l d who come f o r a p e r i o d o f s e v e r a l y e a r s t o be engaged i n b a s i c and i n t e r d i s c i p l i n ary s t u d i e s o f a r t h r o p o d s o f a g r i c u l t u r a l and m e d i c a l importance. An u n u s u a l system adopted a t ICIPE i s t h a t of V i s i t i n g D i r e c t o r s o f R e s e a r c h . These 10-15 VDR's from v a r i o u s i n s t i t u t i o n s t h r o u g h o u t the w o r l d pay one t o s e v e r a l v i s i t s a y e a r t o the C e n t r e t o c o n s u l t and d i r e c t (?) the r e s e a r c h . The C h e m i s t r y u n i t has had two R e s e a r c h S c i e n t i s t s (ex-members, D r s . D . L . E l d e r , T . G e b r e y s u s , W . F . Wood, I . Kubo, G . D . P r e s t w i c h ; and

165

In Host Plant Resistance to Pests; Hedin, P.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

166

HOST P L A N T RESISTANCE T O

PESTS

c u r r e n t members, Drs. A. Maradufu and K. W i l s o n ) and one S e n i o r T e c h n i c i a n , A. Chapya; the two VDR's have been J . Meinwald and K. N a k a n i s h i . The s t u d i e s on p l a n t c o n s t i t u e n t s comprise one h a l f o f the work c a r r i e d o u t by the C h e m i s t r y u n i t , the o t h e r h a l f b e i n g s t u d i e s on i n s e c t pheromones and d e f e n s e s e c r e t i o n s (2) .


Bioassay

of Phagostimulants

and

Antifeedants

Two s p e c i e s o f the A f r i c a n armyworm, Spodoptera exempta and S. l i t t o r a l i s , were m a i n l y employed f o r the b i o a s s a y s , e i t h e r by e l e c t r o p h y s i o l o g y o r by t h e l e a f d i s k method. The monophagous S. exempta has l o n g been known as a major graminaceous c r o p p e s t i n E a s t and South A f r i c a , whereas the polyphagous S. l i t t o r a l i s i s a major c o t t o n p e s t . Other s p e c i e s o f the genus Spodop t e r a are d i s t r i b u t e d t h r o u g h o u t the w o r l d and c o n s t i t u t e a major p e s t . However, most o f the a n t i f e e d a n t s i s o l a t e d so far appear t o be s p e c i f i c t o c e r t a i n i n s e c t s . F o r i n s t a n c e , w a r b u r g a n a l (see below) (_3) r which i s one of the most p o t e n t a n t i f e e d a n t s a g a i n s t S. exempta was h a r d l y a c t i v e a g a i n s t Manduca s e x t a (tobacco hornworm) and S c h i s t o c e r c a vaga (vagrant g r a s s h o p p e r ) ( 4 ) . Hence two i n s e c t s w h i c h seem t o have complementary t a s t e senses are c u r r e n t l y used i n our l a b o r a t o r y , namely, E p i l a c h n i a v a r i v e s t i s (Mexican bean b e e t l e ) and S. e r i d a n i a ( s o u t h e r n armyworm) . The most r e v e a l i n g b i o a s s a y f o r f o l l o w i n g phago s t i m u l a n t s and d e t e r r e n t s i s t h a t o f e l e c t r o p h y s i o l o g y w i t h the e i g h t s e n s i l l a a t the t i p o f t h e m a x i l l a r y p a l p ( 5 ) . These c o r r e s p o n d t o t h e t a s t e buds and a r e shown Γη F i g u r e 1 ( s c a n n i n g e l e c t r o m i c r o g r a p h ) . As d e p i c t e d s c h e m a t i c a l l y i n F i g u r e 2, a m i c r o e l e c t r o d e i s i n s e r t e d i n t o the m a x i l l a r y p a l p and another i n t o one of the s e n s i l l u m . The t i p o f the s e n s i l l u m i s b r o u g h t i n t o c o n t a c t w i t h a f i l t e r paper impregnated w i t h t h e t e s t s o l u t i o n , and the s c o r i n g , w h i c h i s r e c o r d e d as i m p u l s e s p e r second, i s done w i t h an o s c i l l o s c o p e . The maximum number o f i m p u l s e s t h a t can be evoked i s o f the o r d e r o f 200. The f u n c t i o n s o f t h e e i g h t s e n s i l l a appear t o d i f f e r b u t the d e t a i l s have n o t y e t been c l a r i f i e d (5) . Most of the compounds d e s c r i b e d i n t h i s a r t i c l e were i s o l a t e d by f o l l o w i n g the f r a c t i o n a t i o n w i t h more conventional bioassays. The l e a f d i s k method i s shown i n F i g u r e 3 (see 6) . L e a f d i s k s made w i t h a 20 mm cork b o r e r a r e immersed f o r 2 seconds i n the t e s t a c e t o n e s o l u t i o n ; immersion f o r l o n g e r than 2 seconds s h o u l d be a v o i d e d because the p h a g o s t i m u l a n t s (see below) are ex t r a c t e d out. These a r e p l a c e d i n a P e t r i d i s h w i t h con-



11.

KUBO

A N D NAKANISHI

Insect Antifeedants

and

Repellents

167

Figure 1. Scanning electromicrograph (X1650) of tip region of African armyworm (Spodoptera exempta) larva. The maxillary palp of eight sensilla are seen.

Spodoptera exempta

Feeding

Stimulants

sucrose inositol adenosine

Figure 2.

Schematic of electrophycological experiment with sensilla


168

HOST P L A N T RESISTANCE T O PESTS

Spodoptera exempta S. littoralis (African army worms)


Zea mays "~

Test

Ten Insect larvae I

Observation Acetone or Hexane

2, 4, 6, 8, 10, 12, 24, 48 hours Control disks were eaten usually within 2 hours (CHOICE Test)

Figure 3.

The leaf disk bioassay—a "choice" method

t r o l l e a f d i s k s and t e n t h i r d i n s t a r l a r v a e o f S. exempta. T h i s c o n s t i t u t e s a " c h o i c e " t e s t , whereas d e l e t i o n o f t h e c o n t r o l d i s k s c o n s t i t u t e s a "no c h o i c e " test. The s c o r i n g i s c a r r i e d o u t o v e r a p e r i o d o f up t o 2 days depending on t h e a n t i f e e d a n t p o t e n c y . A l t e r n a t i v e l y , t h e sample s o l u t i o n c a n be a p p l i e d d i r e c t l y o n t o s e v e r a l l e a v e s o f p l a n t i n a p o t and scored against c o n t r o l leaves. A f u r t h e r method o f b i o a s s a y i s t o c o a t t h e sample on s t y r o f o a m l a m e l l a e and measure t h e w e i g h t d i f f e r e n c e between u n t r e a t e d l a m e l l a e . The e l e c t r o p h y s i o l o g i c a l method has c l a r i f i e d t h e sugar r e c e p t o r s on S. exempta l a r v a l s e n s i l l a (j>) , and by f o l l o w i n g s y s t e m a t i c f r a c t i o n a t i o n s , two o f t h e p h a g o s t i m u l a n t s c o n t a i n e d i n maize l e a v e s have been i s o l a t e d and c h e m i c a l l y c h a r a c t e r i z e d as s u c r o s e and adenosine ( 7 ) . An i m p o r t a n t f i n d i n g from t h e sugar


11.

KUBO

AND

NAKANISHI

Insect Antifeedants

and

Repellents

169

r e c e p t o r e x p e r i m e n t s i s the f a c t t h a t a few c o n t a c t s o f the s e n s i l l a w i t h f i l t e r paper impregnated w i t h p o t e n t a n t i f e e d a n t s such as w a r b u r g a n a l l e a d t o i r r e v e r s i b l e l o s s o f t a s t e r e s p o n s e ; i n a d d i t i o n , the a n t i f e e d a n t a c t i v i t y o f w a r b u r g a n a l i s i n h i b i t e d by a d d i t i o n o f an e q u i m o l a r amount o f the S H - c o n t a i n i n g L - c y s t e i n e (1).


Antifeedants F o r the sake o f s e l f - d e f e n s e , i t i s not a t a l l s u r p r i s i n g t h a t p l a n t s would c o n t a i n i n s e c t a n t i f e e d a n t s , as w e l l as p e s t i c i d e s and r e p e l l e n t s (7a). S i n c e t h e l i f e cycle o f an i n s e c t i s deranged i f the up-take o f exogenous m o u l t i n g hormones (ecdysones) f a r exceeds the b i o s y n t h e t i c l e v e l , t h e wide o c c u r r e n c e i n p l a n t s o f compounds w i t h m o u l t i n g hormone a c t i v i t y (phytoecdysones) ( 8 ^ , 1 0 ) presumably i s a l s o a s e l f - d e f e n d i n g e v o l u t i o n a r y development. W i t h the u n d e r s t a n d i n g t h a t the term f e e d i n g i s not c l a r i f i e d w i t h i n s e c t s , i . e . , i t may i n v o l v e b i t i n g and/or swallowing f a c t o r s , we would l i k e t o b r o a d l y d e f i n e i n s e c t a n t i f e e d a n t s as s u b s t a n c e s which when t a s t e d can r e s u l t i n c e s s a t i o n o f f e e d i n g e i t h e r t e m p o r a r i l y o r permanently depending upon p o t e n c y (3>) · Some n a t u r a l l y o c c u r r i n g a n t i f e e d a n t s which have been p u b l i s h e d a r e : g l y c o s i d e s o f s t e r o i d a l a l k a l o i d s , d e m i s s i n e (11), s o l a c a u l i n e (12), t o m a t i n e (13), l e p t i n e s I and I I (14); r i n g A enone and/or r i n g D a r o m a t i c s t e r o i d s , the n i c a n d r e n o n e s and o t h e r s (15, 16,Γ7,19^); j u g l o n e (5-hydroxynaphthoquinone) (19); the i s o q u i n o l i n e a l k a l o i d i s o b o l d i n e (6); p h e n y l p r o p a n o i d s (20); germacrane s e s q u i t e r p e n e s s h i r o m o d i o l and s h i r o mol (21,22) ; e n t - c l e r o d a n e and c l e r o d a n e d i t e r p e n e s , c l e r o d e n d r i n (23) , c a r y o p t i n and o t h e r s (24), and the h y d r o x y l a t e d s t e r o i d m e l i a n t r i o l (25). The c o l l e c t i o n s i n E a s t A f r i c a were c a r r i e d o u t on the b a s i s o f i n f o r m a t i o n g a t h e r e d from books (26,27) and e s p e c i a l l y from l o c a l p e o p l e on i n s e c t - r e s i s t a n t plants. In f a c t , some o f the p l a n t s a r e w i d e l y used t o c o n t r o l pest i n s e c t s or f o r medicinal purposes. The e x t r a c t i o n s were f o l l o w e d by b i o a s s a y s , and s t r u c t u r e s were d e t e r m i n e d by a c o m b i n a t i o n o f v a r i o u s s p e c t r a l methods combined o c c a s i o n a l l y w i t h c h e m i c a l r e a c t i o n s . a) A z a d i r a c h t i n from Leaves and B e r r i e s o f A z a d i r achta"""Indica ( I n d i a n neem t r e e ) and tlaLia, a z e d a r a c h (28). The t r e e s o c c u r commonly i n I n d i a and E a s t and West A f r i c a and are w i d e l y used f o r chewing s t i c k s f o r c l e a n i n g the t e e t h and as a remedy a g a i n s t m a l a r i a . The S c h i s t o c e r c a g r e g a r i a ( d e s e r t l o c u s t ) a n t i f e e d a n t m e l i a n t r i o l (25) was i s o l a t e d from the l e a v e s . Azadir a c h t i n was a n o n c r y s t a l l i n e compound reknown f o r i t s


170


PESTS

very strong antifeedant p r o p e r t i e s a g a i n s t S. g r e g a r i a , i . e . , 100% i n h i b i t i o n of feeding i s caused by 40 y g / l , o r when impregnated on f i l t e r paper by 1 ng/cm AcO' (29,20). A l t h o u g h p a r MeOOC t i a l s t r u c t u r e s and the c o r r e c t molecular formula Azadirachtin 35 44°l6 forwarded (29), c o m p l e x i t y o f the s t r u c t u r e e l u d e d e l u c i d a t i o n w i t h o u t t h e usage o f CMR. The s t r u c t u r e i s based on e x t e n s i v e NMR s t u d i e s on a z a d i r a c h t i n and i t s 14-monoa c e t a t e ( p r o b a b l y formed by a c y l m i g r a t i o n from 7-OH), i n p a r t i c u l a r the t e c h n i q u e o f simultaneous p a r t i a l l y r e l a x e d F o u r i e r t r a n s f o r m (PRFT) and o f f - r e s o n a n c e d e c o u p l i n g , which was used f o r the f i r s t t i m e . It is a l i m o n o i d c o n t a i n i n g a c l e a v e d C r i n g and an u n s t a b l e d i h y d r o f u r a n moiety. I t i s one o f t h e most p o t e n t a n t i f e e d a n t s a g a i n s t S. exempta ( r o u g h l y o n e - h a l f o f the warburganal p o t e n c y ) . The s t r u c t u r e i s t o o complex t o be s y n t h e s i z e d on a p r a c t i c a l l e v e l b u t s i n c e the y i e l d i s q u i t e h i g h (we were a b l e t o o b t a i n 800 mg from 300 g o f seeds) and the t r e e i s easy t o c u l t i v a t e , p r a c t i c a l usage o f the neem t r e e may not be o u t o f the q u e s t i o n . b) X y l o m o l i n from U n r i p e F r u i t s o f X v l o c a r p u s mpluccënsls. Roem. (Meliaceae) ( 3 1 , 3 Τ Π The u n r i p e f r u i t s (weighing about 200 g) COOCH. are b i t t e r b u t the r i p e f r u i t s a r e t r e a s u r e d by ..OCH^ E a s t A f r i c a n s and are r e p u t e d t o have a p h r o d i s i a c p r o p e r t i e s . Since a l l o f the s k e l e t a l p r o t o n s are c o n t i g u o u s , PMR e l u c i d a t e d the e n t i r e Xylomolin p r o t o n system. The con f i g u r a t i o n s a t c h i r a l c e n t e r s a r e based on the f a c t s t h a t no J v a l u e s were l a r g e r than 3 Hz, and n e i t h e r NOE nor W-type c o u p l i n g s c o u l d be o b s e r v e d . Presence o f the a c e t a l i c methoxyl group was deduced from the p r e s ence o f a d o u b l e t o f q u a r t e t s s i g n a l i n the undecoupled CMR spectrum; t h i s i s due t o a d d i t i o n a l c o u p l i n g o f the methoxyl carbon t o 3-H. I t i s a s e c o i r i d o i d with a s t r u c t u r e c l o s e l y r e l a t e d t o s e c o l o g a n i n , the o r i g i n o f the t e r p e n o i d d e r i v e d m o i e t i e s i n i n d o l e a l k a l o i d s . It i s possible that xylomolin i s a progenitor of alkaloids which may be c o n t a i n e d i n the r i p e f r u i t s b u t t h i s has n o t been i n v e s t i g a t e d . The a n t i f e e d a n t l e v e l i s moder2


C

H

w

e

r

e


11.

KUBO

A N D NAKANISHI

Insect Antifeedants

and

Repellents

171

12


Ar-I

Ar-H

Ar — III

a t e , i . e . , 100 ppm a g a i n s t S. exempta; i t s t r o n g l y i n h i b i t s the r e s p i r a t i o n o f r a t l i v e r mitochondria. c) A j u g a r i n s from Aiucra remota ( L a b i a t a e ) Leaves (33). As quoted above, o t h e r c l e r o d a n e a n t i f e e d a n t s have been i s o l a t e d p r e v i o u s l y (23,24) . However, i t i s i n t e r e s t i n g t o note t h a t b o t h a n t i p o d a l s k e l e t o n s a r e a c t i v e , as e x e m p l i f i e d by c l e r o d e n d r i n (23), an e n t c l e r o d a n e d i t e r p e n e , and c a r y o p t i n (24), a c l e r o d a n e diterpene. The a b s o l u t e c o n f i g u r a t i o n o f t h e a j u g a r i n s ( e n t - c l e r o d a n e ) was d e t e r m i n e d (3J3) by c o n v e r s i o n t o a 6-keto compound and comparing i t s CD w i t h a r e f e r e n c e compound d e r i v e d from c l e r o d i n (24). The a n t i f e e d a n t a c t i v i t y i s 100 ppm a g a i n s t S. exempta. d) H a r r i s o n i n from Leaves o f H a r r i s o n i a a b v s s i n i c a O i v (Simarubaceae) ("Msabubini" o r "Mpapura-doko" i n T h i s shrub i s used w i d e l y i n E a s t Swahili) (34) A f r i c a n f o l k remedies i n c l u d i n g treatment f o r bubonic p l a g u e , hemorrhoid, snake b i t e , etc. The chopped r o o t (650 g) gave 70 mg o f h a r r i s o n i n and 25 mg o f obacunone, a r e l a t e d limonoid b i t t e r p r i n c i p l e (35, 36). The s t r u c t u r e was d e t e r mined by e x t e n s i v e NMR s t u d i e s , e s p e c i a l l y CMR (PND, PRFT and 28H undecoupled) and comparisons o f peaks w i t h t h o s e o f obacuHarrisonin


172


TESTS


none. A l t h o u g h i t was not c l e a r whether the h e m i k e t a l f u n c t i o n a t C-7 was an a r t e f a c t o r n o t , subsequent s t u d i e s have shown t h a t the n a t u r a l p r o d u c t i s a 6,7alpha-diketone. The S. exempta a n t i f e e d a n t a c t i v i t y i s 20 ppm; i t a l s o e x h i b i t s a n t i b i o t i c a c t i v i t y (5 yg/ml a g a i n s t B a c i l l u s s u b t i l i s ) (37) and c y t o t o x i c i t y (2.2 yg/ml, KB t e s t ) (WT. e) P o l y g o d i a l , U g a n d e n s i d i a l and Warburganal from the Bark o f W a r b u r a i a s t u h l m a n n i i and W. u a a n d e n s i s (39).

Polygodial

Warburganal

Ugandensidial

The b a r k s o f b o t h t r e e s are t r e a s u r e d i n f o l k m e d i c i n e and a l s o as f o o d s p i c e . W. s t u h l m a n n i gave the known p o l y g o d i a l (40,41,42) i n moderate y i e l d w h i l e W. ugand e n s i s gave the known u g a n d e n s i d i a l (43) and new warburganal. The y i e l d o f the l a t t e r two are n o t o n l y low b u t t h e y are d i f f i c u l t t o s e p a r a t e , even by h p l c , from a n o t h e r c o n s t i t u e n t and t h i s l e d t o c o n f u s i o n i n s t r u c t u r a l s t u d i e s . Of the t h r e e , w a r b u r g a n a l i s by f a r the most a c t i v e a n t i f e e d a n t (0.1 ppm a g a i n s t S. exempta), b u t more e x t e n s i v e s t u d i e s w i l l have t o depend on s y n t h e t i c m a t e r i a l because o f the l i m i t e d q u a n t i t y . Some s t r u c t u r e / a c t i v i t y s t u d i e s c a r r i e d o u t w i t h the simple p o l y g o d i a l i n d i c a t e d t h a t the a c t i v i t y was l o s t when one o r b o t h a l d e h y d e s were r e d u c e d t o h y d r o x y l groups o r o x i d i z e d t o c a r b o x y l groups. E p i m e r i z a t i o n o f the e q u a t o r i a l 9B-CHO t o the more s t a b l e a x i a l 9a-CHO a l s o r e s u l t e d i n l o s s o f a c t i v i t y (the e q u a t o r i a l epimer p r o b a b l y owes i t s i n s t a b i l i t y t o d i p o l e - d i p o l e r e p u l s i o n between the two aldehyde f u n c t i o n s ) . These r e s u l t s i n c o n j u n c t i o n w i t h the b l o c k i n g o f a n t i f e e d a n t a c t i v i t y upon a d m i n i s t r a t i o n o f an e q u i m o l a r amount o f c y s t e i n e (1) s u g g e s t t h a t a t l e a s t p a r t o f the a n t i f e e d a n t a c t i v i t y i n the case o f S. exempta i s c a u s e d by M i c h a e l type a d d i t i o n o f the e l e c t r o p h i l i c a n t i f e e d a n t t o a n u c l e o p h i l i c t e r m i n a l i n the r e c e p t o r s i t e , and t h a t , as shown by the h i g h a c t i v i t y o f war-


11.

KUBO

A N D NAKANISHI

Insect Antifeedants

and

Repellents

173


b u r g a n a l , t h e s t r u c t u r a l c o m p l e x i t y o f w h i c h i s i n between those o f t h e o t h e r two, t h e s t e r i c r e q u i r e m e n t of the receptor s i t e i s f a i r l y s e l e c t i v e . Interestingly, the a n t i f e e d a n t s a g a i n s t t h e armyworm t a s t e s p i c y t o the human tongue. f) I n f l e x i n from Leaves o f i s o d o n i n f l e x u s ( L a b i a teae) (44) and Isodomedin from Leaves o f I. s h i k o k i a n u s v a r intermedins. (45) . These two compounds^ were i s o l a t e d

AcO

AcO

inflexin

4

isodomedin

from Japanese s o u r c e s b u t a r e quoted here because t h e y b o t h e x h i b i t a n t i f e e d a n t a c t i v i t y as t e s t e d a g a i n s t t h e A f r i c a n armyworm. They a r e a l s o c y t o t o x i c , t h e l e v e l s o f i n f l e x i n and isodomedin b e i n g L D 5.4 yg/ml and 4.0 yg/ml, r e s p e c t i v e l y . They a r e e n t - k a u r e n o i d d i t e r p e n e s with c l o s e l y r e l a t e d structures. g) C r o t e p o x i d e from Leaves o f C r o t o n m a c r o s t a c h y s (46). The a n t i f e e d a n t p r i n c i p l e was i s o l a t e d a c c o r d i n g t o t h e b i o a s s a y w i t h S. exempta and t h e s t r u c t u r e was d e t e r m i n e d by d e t a i l e d NMR and o t h e r methods. To o u r s u r p r i s e the s t r u c t u r e was t h a t l_IQ o f c r o t e p o x i d e (47,48, 49), a compound e x h i b i t ing tumor-inhibitory, a n t i l e u k e m i c and a n t i 0 biotic activity. The c y t o t o x i c i t y and a n t i OGluc feedant a c t i v i t y are b o t h dependent, a t l e a s t p a r t i a l l y , on t h e r e a c Crotepoxide t i o n between t h e n u c l e o 5 0

'Mr


HOST P L A N T RESISTANCE

174

T O PESTS


p h i l i e r e c e p t o r and e l e c t r o p h i l i c moiety o f t h e a c t i v e m o l e c u l e ; i s o l a t i o n o f t h e same m o l e c u l e b y two t o t a l l y d i f f e r e n t b i o a s s a y s proves the s i m i l a r i t y i n c e r t a i n a s p e c t s o f t h e s e two s e e m i n g l y d i f f e r e n t a c t i v i t i e s . h) Unedoside from t h e bark o f Canthium e u r o i d e s (50). Structure determination o f the antifeedant contained i n t h i s Ο p l a n t t u r n e d o u t t o be t h e known u d e s i d e which had been CHoOC i s o l a t e d from A r b u t u s unedo (51) · ,OAc

OAc

Unedoside

i ) Prep LC o f Crude P l a n t E x t r a c t s ( 5 2 ) .

3

EtOAc/hexane 1=4

1 ·' mixture (19) 4 : mixture (l80mg) OCHj

5 : pure compound (40 mg)

[

Host Plant Resistance to Pests

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